The invention is applicable more especially to the manufacture of paper products such as domestic or sanitary papers. Among these in particular are papers entailing direct contact with the skin and repeated rubbing against the skin, for example disposable paper handkerchiefs, toilet paper or any other paper product for wiping the skin, for removing make-up, dry linen, etc.
People afflicted with colds, influenza or various allergies causing nasal flow will wipe their noses frequently. Oftentimes such people's noses are irritated and red because of skin hypersensitization from this nasal flow. For practical reasons, such people use conventional paper handkerchiefs available commercially in the form of boxed handkerchiefs, also called "facial" tissue, or folded handkerchiefs in small cases. Following several sequential nose wipings with these handkerchiefs, the skin at and around the nose becomes increasingly irritated, even inflamed and painful. Consequently, the surface of these handkerchiefs must be softened in order to limit, even suppress any irritation caused by rubbing the handkerchief surface against the skin. Ideally, the feeling should be the softness offered by a cloth handkerchief that has just been washed and pressed.
In another field, namely that of toilet paper, the same softness is required for repeated contacts with the skin taking place with simultaneous rubbing. In particular as concerns persons suffering from skin irritation in the anal region or in the case of hemorrhoids, a toilet paper with a somewhat rough feel will only further irritate the skin when this paper is pressed against this skin.
Accordingly, endeavors have been underway to generally soften the paper sheets or products, such as the tissue paper webs, using a variety of mechanical or chemical means.
As regards the mechanical means, techniques have been developed to improve in particular the appearance and the surface condition of the paper sheet by endowing it with a more slippery feel. In the case of handkerchiefs illustratively, the sheet is calendered to flatten the crests formed when creping the sheet. Also the sheet surface may be frictionally treated in order to eliminate all roughnesses. However, these approaches often are insufficient. European Patent No. 0 029 269 describes a particular manufacturing procedure for such a sheet wherein the nature of the suspensions of fibers forming the various sheet layers, as well as the combination of these layers among each other, are significant factors for the desired velvety feel. However, this procedure limits the selection of appropriate fibers and entails constraints in the first stages of the wet process phase.
The expression "chemical means" covers any softening composition based on one or several chemical compounds. A distinction may be made between two categories of softening compositions. On one hand, the softening additives or compositions which are directly incorporated into the manufacturing pulp or composition or otherwise are applied to a wet web of paper. And, on the other hand, the softening compositions or lotions which are applied to the surface of a product or a sheet of paper in the dry state, i.e., where prior drying has taken place.
In the first case, these additives as a rule are used as fiber debonding agents and thereby allow flexibilizing of the sheet so made. Many patents have been filed in this field, for example, European Patent Application No. A 0 049 924; European Patent No. B 0 347 176; U.S. Pat. No. 2,944,931; U.S. Pat. No. 5,415,737; and International Application No. WO 95/10661.
European Application No. A 0 049 924 discloses the incorporation of a quaternary ammonium compound and at least one nonionic surfactant selected from fatty acid and fatty alcohol ethylene oxide derivatives into the manufacturing composition in order to achieve a soft absorbent paper. The object of European Patent No. B 0 347 176 is a tissue paper comprising at least one non-cationic surfactant applied to a wet web of paper. However, the surfactant may migrate into the sheet inside and wholly clad the fibers thereby loosening them and decreasing tensile strength. U.S. Pat. No. 2,944,931 discloses a process for improving the softness of toilet paper and its feel consisting in adding a stable aqueous emulsion containing from 1 to 90% by wt. lanolin and from 10 to 99% by wt. of a cationic emulsifier, such as quaternary ammonium salts, to the manufacturing composition. U.S. Pat. No. 5,415,737 concerns a finished soft paper product comprising a vegetal oil-based quaternary ammonium ester compound which is also added to the manufacturing composition. International Application No. WO 95/10661 discloses a manufacturing process for a soft paper with improved feel consisting in added fatty acid ester salts of quaternary amine triethanol as softeners in the fiber aqueous suspensions.
However, on the whole as regards these patents, the product or sheet surface does not offer the desired slippery feature. It is only the product or the web as a whole which is more soft. Moreover, the loss of softening composition during the web manufacturing process is more than trivial.
In the same vein, U.S. Pat. No. 5,279,767 describes more specifically a softening composition comprising a mixture of a quaternary ammonium compound and a polyhydroxy compound. This composition is prepared by mixing in a first stage these two compounds at a high temperature at which they are miscible and then diluting the mixture in high temperature water in order to form an aqueous dispersion of vesicles (or micelles). This composition is preferably incorporated into the manufacturing composition and may be applied to the surface of the formed web, when wet, before drying. It is believed in this patent that the vesicles break up at the time of drying. Most of the polyhydroxy compound so "released" penetrates into the interior of the cellulose fibers and improves the fiber flexibility, the other part being retained at the fiber surface and increases the absorbency rate of fibers. Because of the ionic bonds, the quaternary ammonium compound remains at the surface of the cellulose fibers and thereby the product softness and feel can be improved. This patent does not mention a slippery feel in spite of improved softness. This type of compound addresses an increase in fiber flexibility and it acts substantially within the internal sheet structure, not directly and mainly at the sheet surface.
Variations of this composition are described in other patents such as International Application Nos. WO 94/29,520 and WO 94/29,521.
In the second case, the softening compositions are meant to be applied directly to the product surface or to the absorbent paper sheet surface that was previously dried. Their main function is as a skin emollient.
Many patents illustrate this kind of lotion.
For example, with respect to toilet paper or paper towels used in proctology, U.S. Pat. No. 3,264,188 and French Patent No. 2,376,650 describe lotions providing a fatty feel. The latter patent describes a skin wiping paper product treated with a lipophilic and cleaning emollient, the composition being substantially non-polar and non-aqueous. This emollient may be a mineral oil, petrolatum, paraffin waxes, fatty acids, fatty alcohols, fatty acid esters, derivatives of glycerides, lanolin, polysiloxanes and the like. The emollient settles on the skin surface where it forms a thin film. It allows cleaning of the skin by removing soil. Furthermore, U.S. Pat. No. 4,481,243 has as its object a two ply sheet. An emollient which provides a fatty feel is spread over a large part of the sheet surface. However, the emollient is not applied in a zone where the plies are combined by embossing.
Silicone oils, such as polysiloxanes, may be applied to a tissue paper web in the manner disclosed in European Patent Nos. 0 347 153 and 0 595 994, and in European Patent Application No. 0 656 971. However, some silicone oils are hydrophobic and lower the wettability at the surface of the paper so treated.
The object of U.S. Pat. No. 3,305,392 is a sheet of paper to the surface of which an emollient has been applied by displacing the sheet over a comparatively solid block of an emollient composition similar to wax. This composition comprises a lubricating and softening portion such as zinc stearate; aluminum-, sodium-, calcium- or magnesium-stearate; stearic acid; esters of palmitic or spermacetic acid; stearic alcohol; and where called for additionally esters of stearic and lauric acid polyethylene glycol as effective lubricants. Compounds such as oleic acid, mineral oil, tallow glyceride, distearyl methylamine, primary and secondary fatty amines and derivatives of lanolin, which allow the composition to assume a plastic shape, may also be added. In order to reduce the migration of the compounds inside the sheet, agents may also be provided that contain an active group affixing itself on the cellulose fibers, these agents being cationic. Because this kind of composition is in a fairly solid state, it can be used only at lower speeds and the applied quantities will not be optimized by such techniques.
There are other patents which also relate to lotions which at ambient temperature are solid or semi-solid. U.S. Pat. No. 3,896,807 describes an emollient composition in the form of a non-adhesive and non-oily solid. This composition is heated or admixed with non-aqueous solvents of the type such as acetone, chloroform, trichloroethylene, xylene, xylol and other aromatic solvents in order to be impregnated in liquid form onto a substrate, for example, made of paper. Accordingly, this composition requires for application either heating means or solvents which for the most part for toxicological reasons cannot be used. The main components of this composition are an oil phase containing an oil material, such as mineral oil, petrolatum, paraffin, vegetal oil and different animal oils, and possibly emollients such as cetyl alcohol, propylene glycol, glycerin, triethylene glycol, waxes, and an emulsifier. This kind of lotion is significant because when moisture makes contact with the skin, this composition forms an oil emulsion in water to act as an emollient.
A more recent International Patent Application, namely WO 95/16824, furthermore suggests an anhydrous lotion which is solid or semi-solid at 20.degree. C. but which entails constraints regarding its application to a sheet. This procedure assumes heating means and all the accompanying problems both with respect to the material selected for impregnation and the liquid and stable state of the lotion which in this procedure must remain at a fairly constant temperature.
Some emollients, such as lanolin, incur drawbacks linked to their odor or to the fact they decrease the sheet absorbency. European Patent No. 0 365 726 attempts to remedy these problems by proposing lotions with a single water-soluble component, namely lauroamphoglycinate, quaternary ammonium homo- or copolymeric derivatives, a triquaternary phospholipidic complex or a glutamate glucose complex.
French Patent No. 2,538,238 describes a process in which a substrate, for example a strip of paper from which paper towels will be made, passes through a lotion dissolved in an organic solvent and where this solvent then is caused to evaporate. The substrate furthermore may be impregnated practically up to saturation with an aqueous emulsion of which the ingredients are absorbed by the substrate and then dried to completely eliminate the water from the emulsion. The lotion contains a surfactant compound and a fatty body. The two above mentioned procedures entail subsequent evaporation or drying stages that preferably are avoided when manufacturing tissue paper webs.
Once applied, some lotions modify the physical and mechanical properties of the absorbent paper products or of the sheet of paper, such as absorbency, tensile strength in the direction of advance and in the transverse direction, etc. It is especially important that a lotion-impregnated product maintain the best possible strength properties as the same product to which no lotion is applied.